Despite lingering concerns that using fertility drugs might raise a woman's chances for later developing ovarian cancer, new research suggests the drugs don't contribute any added risk.

"One important message is women who need to use fertility drugs to get pregnant should not worry about using these fertility drugs," said Dr. Albert Asante, lead author of the study and a clinical fellow in the division of reproductive endocrinology at the Mayo Clinic in Rochester, Minnesota.

Research on fertility drugs and cancer risk has yielded conflicting results. Some studies, especially in the 1990s, showed an increased likelihood of the cancer among women who took fertility drugs. And a Dutch report from 2011 found an increase in borderline tumors -- those with abnormal cells that might not turn into cancer.

However, Dr. Bert Scoccia, a professor at the University of Illinois School of Medicine in Chicago who studies fertility medication and cancer, said numerous other studies have found no increased risk for women who take fertility boosting medications.

The majority of studies have pointed to fertility drugs being safe, but many of them were conducted outside the U.S., Asante noted. "It's difficult to translate what those findings mean for women in the U.S.," he told Reuters Health. So Asante and his colleagues gathered medical information on 1900 women from an ongoing ovarian cancer study at the Mayo Clinic.

The researchers compared 1,028 women with ovarian cancer to 872 women of similar age who did not have cancer.

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About 24 percent of the women who did not have ovarian cancer reported having used fertility drugs, while roughly 17 percent of women who had ovarian cancer had used fertility drugs, the team reports in the medical journal Fertility and Sterility.

After taking into account factors that can influence the risk for ovarian cancer, such as age and use of the birth control pill, the researchers found no difference in cancer rates between the groups. "That is reassuring," said Scoccia, who was not involved in the research. Scoccia said it's possible that the type of fertility drugs women used decades ago could explain why some earlier studies had found opposite results.

"Unfortunately, because the patients (in this study) were providing the information in a questionnaire, we don't know what drugs they took. Nevertheless...there was no increased risk in ovarian cancer," said Scoccia.

It's been difficult to tease out the effects of fertility drugs on ovarian cancer because women who are infertile are already considered to be at a higher risk for the cancer.

Infertility, defined as not getting pregnant after a year of trying, is experienced by about 15 percent of couples. Asante's team looked specifically at whether women in the study who reported being infertile -- whether or not they had taken fertility drugs -- had a greater chance of developing ovarian cancer, and found no added risk.

Asante said one explanation for the result is that most of the women in his study had infertility issues, but eventually became pregnant. He would still expect to see a higher risk of ovarian cancer if he had included more women who never ended up having a baby.

Asante left open the possibility that long term use of fertility drugs -- more than one year -- could impact the chance of developing ovarian cancer, and to be safe these women might benefit from additional monitoring for tumors.

He said that because ovarian cancer is rare and develops later in life, there is a need for longer studies to thoroughly assess the effect of fertility drugs.

According to the National Cancer Institute, close to 13 out of every 100,000 women develop ovarian cancer, most commonly in their 60s. Family history of the disease or certain gene mutations raise a woman's risk considerably.

Scoccia said the recommendation for fertility drug use is that women use the lowest possible dose for the shortest amount of time.

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